"...there is no more perfect form of subjection than the one
that preserves the appearance of freedom." -- Rousseau

Monday, February 13, 2012

Tons of Fun: Humpbacks in Hawai'i

They're back!

Each winter Hawai'i gets thousands of repeat visitors, many of them of the species Humanica Snowbirdae, giving a much appreciated boost to our economy. The visitors I look forward to the most, however, don't spend a dime. They weigh an average of 40 tons and are the size of a bus. I'm referring to Megaptera Novaeangliae, or Humpback whales, who come here for some of the same reasons as Humanica Snowbirdae; the warm clear ocean waters, idyllic weather, romantic mating habitats.

However, the Humpbacks differ in several respects from most Snowbirdae. For one thing Humpbacks give birth here to their 1-ton 12-foot long calves. The actual moment of birth of a Humpback is still something of a mystery -- no one has been able to document the event itself. Nor are scientists certain why the whales don't just stay in their home territory of Alaska to give birth rather than swimming 2,000 miles to Hawai'i. One reason may be that the shallow warm waters around the Hawaiian Islands are a safer nursery for the babies because they can escape predation from Orca whales, who don't often range this far south, but no one knows for sure.

Another difference between Humpbacks and other visitors is that the Humpbacks don't eat during the entire time they are here, whereas Humanica Snowbirdae are noted for their enthusiastic consumptive behavior. The Humpbacks' diet consists mostly of tiny plankton and krill as well as small fish like mackerel which aren't found in enough abundance in Hawaiian waters to sustain them. This 2-3 month starvation diet is particularly hard on new mothers, whose fat reserves have to be enough for both them and for their newborn calves to develop strength and stamina for the arduous trip back to Alaska. Maybe for this reason females are larger than males, one of the few mammals for which this is the case.

Humpbacks seem to have a lot of fun while they are here, like many other visitors do. But Humpback "fun" can be very dramatic, particularly when they breach, launching themselves almost completely out of the water and landing with an impressive splash visible for miles. You can imagine the strength it must take to propel 40 tons of blubber straight up out of the water -- and I've seen individuals do this repeatedly for 20-30 times. They also like to slap their pectoral fins or their tail flukes on the surface making a tremendously loud noise. Scientists think this behavior is associated with courtship and social dominance, but in their home feeding grounds Humpbacks also use these behaviors to cooperatively round up food. Whatever the reason, it sure looks like they're having a great time.

One of the most widely known behaviors of Humpbacks is their singing. But most people aren't aware that (a) only the males sing and (b) nearly all singing takes place just before and during migration and while the whales are here in their breeding grounds. The strange underwater sounds that sailors heard for centuries weren't identified as coming from Humpbacks until the 1960's, when they began to be studied scientifically. Here are a few of the recent findings detailed by the conservation organization Whale Trust:

A typical song is ... made up of 5-7 themes that are usually repeated in a sequential order. A song typically lasts 8-15 minutes (although it may range from 5-30 minutes), and then is repeated over and over in a song session that may last several hours... A striking feature of the song is that it gradually changes or evolves over time. Each year, different sounds and arrangements of sounds form to create new phrases or themes. These changes are slowly incorporated into the song, while some older patterns are lost completely...The change in the song display seems to occur in a collective or common way throughout the population. Usually after a period of several years, the song is virtually unrecognizable from the original version. In some cases, however, the song has completely changed in just two years! Despite the constantly changing nature of the song, all singers in a population sing essentially the same version at any one time. In fact, all the singers in the North Pacific (that is, whales in Japan, Hawaii, Mexico and the Philippines) separated by thousands of kilometers sing essentially the same version of a song at any one time...The explanation for the collective change of the song, especially over such vast distances, is currently unknown.

Humpbacks were nearly driven to extinction by relentless hunting during the 1800's and early 1900's. Hundreds of thousands were slaughtered during this time for their oil, meat, and bones. During the period 1910-1916 more than 60,000 humpbacks were killed just in the southern hemisphere. The North Pacific population was reduced to just 1,000 animals at the lowest point. They have been protected for about the past 50 years and have made a slight comeback, with the current world-wide population about 6-10 thousand, 50% of whom overwinter in Hawai'i.